This invention relates generally to intruder detection systems and is more particularly directed to an improved intruder detection system that is operative to detect the presence of an intruder while being insensitive to extraneous phenomena which have, for a considerable period of time, rendered like intruder detection apparatus virtually useless because of false alarms generated by the existence of extraneous signals which have no relation to the presence or absence of an intruder. Such extraneous signals might include nature generated signals such as lightning, or manmade signals such as might occupy the space around an electrical power transmission facility.
The prior art includes:
__________________________________________________________________________ U.S. Pat. No. Title Patentee Issue Date __________________________________________________________________________ 3,222,664 DETECTION APPARATUS J. Premack Dec. 3, 1965 3,293,631 DETECTION APPARATUS J. Premack Dec. 20, 1966 4,103,252 CAPACITIVE TOUCH- Bobick July 25, 1978 ACTIVATED TRANSDUCER SYSTEM INCLUDING A PLURALITY OF OSCILLATORS 4,169,260 CAPACITIVE INTRUSION Bayer Sep. 25, 1979 DETECTOR CIRCUITRY UTILIZING REFERENCE OSCILLATOR DRIFT 4,222,045 CAPACITIVE SHIFT FIRE Cholin Sep. 9, 1980 DETECTION DEVICE 4,240,528 FIELD SENSOR Kraus Dec. 23, 1980 4,366,473 CAPACITIVELY COUPLED Inoue et al. Dec. 28, 1982 ELECTROMAGNETIC INTRUSION WARNING SYSTEM __________________________________________________________________________